Typically, rotary wing aircrafts like helicopters are sustained by a rotor, rotating about a vertical rotor shaft, generating lift or upward thrust. In a conventional helicopter the thrust from the rotor can be controlled by changing the pitch angle (or in short; the blade pitch) of the rotor blades. The blade pitch is in the field of propeller aerodynamics defined as the lateral angle between the blades and a reference plane perpendicular to the rotor shaft axis, measured perpendicular to the longitudinal axis of a rotor blade.
By collectively changing the blade pitch of all the rotor blades or by changing the rotational speed of the rotor, the helicopter can be controlled in the vertical direction. The horizontal direction of flight and the stability of the helicopter, however, are controlled by cyclically adjusting the pitch means that the blade pitch of each rotor blade is adjusted from a maximum in a particular position of rotation to a minimum at the opposite side. This causes the lift in one part of the rotation to be larger than in other parts, whereby the rotor is tilted with respect to the reference plane. When the rotor (and helicopter) tilts like this, the initially vertical thrust also tilts, and therefore gets a horizontal component pulling the helicopter in the desired direction.
Normally, a helicopter must be actively controlled by a well trained pilot or from gyroscopic sensors and computers. The necessary means to varying and controlling the pitch angle of each blade are normally complicated, expensive and add weight to the helicopter. The blade pitch is typically controlled via a swash plate connected to servos. Because the swash plate need to be positioned accurately with as little friction and playas possible it is complicated and expensive. On most helicopters the swash plate has a rotating part and a non-rotating part connected together with a large ball bearing. The rotating part of the swash plate is again connected to the rotor blades via a set of links and other mechanical components.
Alternative solutions employing actuators connected to rotor blade control surfaces or magnetic coil systems acting directly on a permanent magnet mounted on a rotor blade pitch arm have been tested. These systems are typically not precise enough and lack the necessary accuracy or they are heavy and require a lot of power to operate properly.
To maintain good and precise control over the rotor blade in a helicopter would require a completely new swash plate system.